Many different designs of rotary pumps exist, some having rotating members which rotate beside one another, known as exterior rotor pumps, and other pumps having only a single rotor. Other rotary devices have two components with unequal numbers of teeth. They rotate at two different speeds. These are generally known as gerotors.
The particular class of pump to which the present invention relates has two rotary components, namely an inner rotary component and an outer rotary component, with the inner rotor being located within the outer rotor. Such pumps are generally known as internal rotor pumps. In this type of pump, both the inner and outer rotor rotate together in unison in the same direction at the same speed. The inner rotor and the outer rotor rotate about respective inner and outer rotor axes which are spaced apart from one another. Thus as the two rotors rotate, the volume defined between the inner and the outer rotors will vary from a minimum to a maximum and back to a minimum.
Generally speaking, such internal rotor pumps are based on a concept in which the inner rotor defines a series of recesses and abutments, and the outer rotor also defines a series of recesses and abutments, and the abutments on the outer rotor fitting within and sweeping around the recesses in the inner rotor, and vice versa.
The problem in the design of all such internal rotor pumps is that of achieving a satisfactory seal between the abutments on one rotor and the surfaces of the other rotor. Such internal rotor pumps are to be distinguished from other rotary devices including proposals for both pumps and motors in which the outer component is stationary, and only the internal rotor rotates. These rotary devices present a somewhat different set of problems since the inner rotor must actually orbit within the outer stationary component.
One form of internal rotor pump is disclosed in U.S. Pat. No. 5,066,207, Inventor V. K. Valavaara. In this design, the abutments on the outer rotor were of cylindrical shape, and the recesses in the inner rotor were of generally semi-cylindrical shape. While this form of internal rotor pump has certain advantages from the viewpoint of manufacturing solutions, in practice, it left certain problems unresolved. In particular, the seals between the inner rotor and the outer rotor were achieved only momentarily. Additional problems were encountered in the volumetric efficiency of the pump. Also the pressures which could be achieved, were not entirely satisfactory.
Another more complex design is shown in U.S. Pat. No. 4,932,850 inventor V. K. Valavaara. This design employs relatively complex shapes for abutments on the inner rotor and also for recesses on the outer rotor. In addition it employs other surfaces of the two rotors to assist in achieving more effective sealing.
This more complex form of rotary pump had an improved performance, and would reach higher pressures. However, its design involved the use of multiple sealing surfaces on the inner and outer rotary components and the manufacture of this pump was consequently somewhat more complex.
An additional feature of such rotary pumps is that the displacement of the pump is essentially a function of the separation of the rotary axes of the inner and outer rotary component. Clearly, the greater the separation between the two axes, the greater is the potential displacement. This in turn affects the efficiency of the pump, as compared with other pumps, of other designs.
The separation of the two axes however has certain practical limits, and there is only a restricted scope for improving pump efficiency simply by increasing the separation. Other principle factors affecting the maximizing of the efficiency of the pump include the shaping of the abutments and recesses of the inner and outer rotors, and the achievement of a satisfactory sealing area as between portions of the inner and outer rotor, at various rotational positions of the two rotors.